| Abstract: | The phase compn. and sintering behavior of two com. available 10 mol % Sc2O3-1 mol% CeO2-ZrO2 ceramics produced by Daiichi Kigenso Kagaku Kogyo (DKKK) and Praxair have been studied. DKKK powders have been manufd. using a wet copptn. chem. route, and Praxair powders have been produced by spray pyrolysis. The morphol. of the powders, as studied by SEM, has been very different. DKKK powders were presented as soft (.apprx.100 micro m) spherical agglomerates contg. 60-100 nm cryst. particles, whereas the Praxair powders were presented as sintered platelet agglomerates, up to 30 micro m long and 3-4 micro m thick, which consisted of smaller 100-200 nm cryst. particles. X-ray diffraction anal. has shown that both DKKK and Praxair powders contained a mixt. of cubic (c) and rhombohedral (r) phases: 79% cubic +21% rhombohedral for DKKK powders and 88% cubic +12% rhombohedral for Praxair powders. Higher quantities of the Si impurity level have been detected in Praxair powder as compared to DKKK powder by secondary ion mass spectroscopy. The morphol. features, along with differences in compn. and the impurity level of both powders, resulted in significantly different sintering behaviors. The DKKK powders showed a more active sintering behavior than of Praxair powders, reaching 93-95% of theor. d. when sintered at 1300 DegC for 2 h. Comparatively, the Praxair powders required high sintering temps. at 1500-1600 DegC. However, even at such high sintering temps., a significant amt. of porosity was obsd. Both DKKK and Praxair ceramics sintered at 1300 DegC or above exist in a cubic phase at room temp. However, if sintered at 1100 DegC and 1200 DegC, the DKKK ceramics exist in a rhombohedral phase at room temp. The DKKK ceramics sintered at 1300 DegC or above exhibit cubic to rhombohedral and back to cubic phase transitions upon heating at a 300-500 DegC temp. range, while Praxair ceramics exist in a pure cubic phase upon heating from room temp. to 900 DegC. However, if heated rather fast, the cubic to rhombohedral phase transformation could be avoided. Thus it is not expected that the obsd. phase transitions play a significant role in developing transformation stresses in ScCeZrO2 electrolyte upon heating and cooling down from the operation temps. [on SciFinder (R)] |
